Tuesday, March 12, 2013

Bash script self-updates from github

Recently the systems engineering team @ Cloud9ers ($dayjob) has been busy building the infrastructure for a very ambitious and large scale project for one of our customers. The project involves tons of distributed programming besides lots of systems work as well. I'd like to share with the community a small tidbit of information. It's often some small things the one sometimes gives a moment to admire, and hereby share!

The problem

  • We are building a private cloud. Ubuntu server instances running on that are cloned from a master template
  • While most clouds provide what I call "Instance Identity" information through some pre-known web service URI, in our case we utilize VMware's "Invoke-VMScript" API to run scripts inside the cloned template, thus customizing it and giving it its identity, then puppet takes it from there. Note that we're using a simple vCenter+ESXi (no vCloud stuff here) no shared storage even!

Ok the real problem

  • Editing the template, and publishing it across the cloud (a topic for another post) takes considerable time! I wanted a way to be able to quickly update my identity scripts without having to re-build and re-publish images


  • A script with a trivially simple (thus mostly fixed) "bootstrap" section, which auto-updates itself from github and relaunches its-new-self!


Nothing ground breaking, but still a cool trick eh! Yeah I could have added a broken this into multiple scripts and maybe run-parts them. Of-course this script is quite basic, but it's meant to remain that way since the heavy lifting is puppet's responsibility!
Note: To run this successfully the user this is run under, should have passwordless sudo rights to run "ip" and to run "itself" :) Got cool ideas, thoughts or comments? Leave me a message

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